The present invention relates to a hydraulic brake system with slip control, wherein at least one wheel brake of an automotive vehicle is connected to a master cylinder, wherein a normally opened inlet valve is inserted in the connection between the master cylinder and the wheel brake which is adapted to be switched into a closed position, and wherein the supply reservoir of the master cylinder includes an opening which is adapted to be tightly closed by a filling device.
When filling such hydraulic brake systems. it is commonly known and conventional practice to generate a relatively high vacuum in the brake system, prior to filling it with brake fluid, by way of the supply reservoir of the master cylinder so that air bubbles in the brake system will be substantially avoided during the subsequent charging with brake fluid. If solenoid valves are provided in the hydraulic brake system for the purpose of a slip-responsive braking pressure modulation, the venting of the brake system will be delayed considerably, since the design of the valves makes them act like throttles. Moreover, filter elements are arranged in the solenoid valves which delay the procedure of venting the brake system. This is particularly apparent with filling procedures in which the filters inserted in the valves are saturated with brake fluid. Normally, the filling is effected in that a filling device is put onto a fill opening of the supply reservoir so as to tightly close the fill opening of the supply reservoir. Thereafter the air enclosed in the brake system is sucked off while the pressure drops. Evacuation of the wheel brake and of the brake lines connected to the wheel brake must be carried out through the inlet valve acting as a throttle.
The period of time between the commencement of the venting procedure and the generation of a vacuum required in the wheel brake is thus predetermined by the throttling effect of the solenoid valve. In addition, the filling procedure succeeding the venting procedure is obstructed in the same manner by the solenoid valve. Consequently, the entire procedure takes a relatively long time particularly in the event of the first charging of a hydraulic brake system during the line assembly.
It is therefore an object of the present invention to improve upon hydraulic brake systems of the type referred to such that the filling procedure can be performed in considerably less time.